Please explain what it is that you want to know...Cyanobacteria is very important, as it produces a great deal of the oxygen we breathe. Plants are also thought to have had a common ancestor with cyanobacteria (That's biospeak for "have evolved from," a saying not really correct, and any biologist will refute the phrase "having evolved from" ).

Photosynthesis did not depend on any one species to form. It happened so on a molecular level within any photosynthetic organism.

Your estimate might be a little conservative =D Cyanobacteria is usually grouped with phytoplankton, and the entire group is responsible for up to 70% of the world's oxygen's release from Carbon Dioxide.

Cyranian wrote:Well, cyanobacteria evolved from eukaryotic chlorolasts, which in turn are found in plants today. And since they produce oxygen as a by-product of photosynthesis, their important role in photosynthesis over millions of years is to basically change our atmosphere from being CO2-rich to O2-rich. Essentially, their ultimate function in the process made what we are today.